
#1
Sep2109, 10:36 AM

P: 18

the landing speed of a jumbo jet is 300Kn/hr. After landing, the jet comes to the safe taxiing speed of 30Km/hr in 12 seconds. The airport authorities would like to keep a saftey margin of 250 metres of runway. How long should the runway be for the safe landing of jumbo jets?
Now, I remember doing this in class. I just can't find my notes. I was thinking that it might have something to do with: Final velocity(v)= initial velocity(u)+acceleration(a) x time(t) maybe rearranging it then being able to find the distance travelled. so: a=(uv)/t all help appreciated 



#2
Sep2109, 10:47 AM

HW Helper
P: 4,442

Your formula for a is correct. Convert km/h to m/s and find the acceleration.
There is a kinematic equation which contains vi,a,t and x. Using that equation find x.To it add safety margin to find the length of the run way. 



#3
Sep2109, 11:16 AM

P: 18

ok. from what you've said this is what i've tried
u=300km/hr=1080m/s v=30km/hr=108m/s t=12s safety margin=250m to get a a=(uv)/t =(1080108)/12 =81m/s so: distance covered=u.t + 1/2.a.t^2 =(1080 x 12) + (1/2 x 81 x 144) =12960 + 5832 =18792m then add the safety margin =18792 + 250 = 19042m = 19.042km am I any closer to the answer do you think? 



#4
Sep2109, 11:21 AM

HW Helper
P: 4,442

finding length of airport runway
Your conversion of km/hr to m/s is wrong.
The plane is slowing down. So the acceleration must be negative. 



#5
Sep2109, 11:32 AM

P: 18

ok so it would be
a=(vu)/t =(1081080)/12 =81m/s so: distance covered=u.t + 1/2.a.t^2 =(1080 x 12) + (1/2 x 81 x 144) =12960 + 360 =12600m then add the safety margin =12600 + 250 = 12850m = 12.85km maybe? 



#6
Sep2109, 12:29 PM

HW Helper
P: 4,442

300km/hr = 300*1000/3600 = ? m/s




#7
Sep2109, 12:58 PM

P: 18

had that the first time and thought i was wrong.
that being the case so: distance covered=u.t + 1/2.a.t^2 =(83.33 x 12) + (1/2 x 6.25 x 144) =999 + 450 =549m then add the safety margin =549 + 250 = 799m = 0.799km you must hate me by now =] 



#8
Sep2109, 07:28 PM

HW Helper
P: 4,442

Now the answer is correct.




#9
Sep2309, 08:42 AM

P: 18

thanks so much rl. you are a legend



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